Circuit protective device



March 29, 1932. END 1,851,739

CIRCUIT PROTECTIVE DEVICE Filed Feb. 17. 1927 /7 Inventor: Z73 George R.Townsend 26 27 His Attorneg Patented Mar. '29, 1932 UNITED STATES ATENT OFFICE GEORGE E. TOWNSEND, OF SCHENECTADY, NEW YORK, ASSIGIIOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK CIRCUIT PROTECTIVE DEVICE Application filed February 17, 1927. Serial No. 169,042.-

tive systems employing such devices.

One of the principal objects of the invention is to provide means for obtaining automatic time delay under voltage circuit protection with any of the usual forms of electroresponsive switches or contactors that are closed and maintained closedv electrically, preferably under master switch control.

Heretofore various types of remotely controlled mechanically latched switches have been em loyed to afford time delay under voltage circuit protection. Such devices necessarily involve special latchmechanism for holding the'switch in the circuit closing position and complicated electroresponsive time delay means for releasing the latch mechanism to permit the switch to operate to the circuit opening position a time interval after the occurrence of undervoltage conditions.-

By means of the present invention the many ditficulties inherent in the latched type of switch are avoided entirely and time delay undervoltage circuit protection readily may be obtained with any standard type of electromagnetic line switch or contactor that is biased to the circuit opening position and electromagnetically operated to and held in the circuit closing position.

Briefly, in accordance with the present invention the electromagnetic line switch or contactor is connected to be energized in accordance with the voltage of the circuit controlled thereby preferably under master push button switch control and a small auxiliary automatic time delay circuit controlling device is provided for opening the energizing circuit of the electromagnetic line switch a time interval after the occurrence of undervoltage conditions.

The auxiliary automatic time delay device is arranged to be operated tothe circuit ClOS'.

ing position by electroresponsive means upon the closin of the electromagnetic line con-' tactor un er the master push button control. Preferably the same electromagnet closes both the line switch and the automatic time delay circuit controlling device. The automatic time delay circuit controlling device 1s arranged to remain in the circuit closing position for the desired time interval after the occurrence of undervoltage conditions. Thus the electromagnetic line switch is free to operate to the circuit opening position in accordance with its bias as soon as the undervoltage condition occurs. Nevertheless since the energizing circuit of the electromagnetic line switch is maintained closed by the automatic time element device,the electromagnetic line switch will return immediately to the circuit closing position in case the undervoltage condition is only momentary. If, however, the undervoltage condition persists, the automatic time delay device functions to interrupt the energizing circuit of the electromagnetic line switch after a predetermined time interval, thereby efiectively preventing automatic reclosure of the electromagnetic line switch when the voltage of the control circuit subsequently becomes normal.

In the accompanying drawings illustrating the preferred embodiments of the invention, Fig. 1 is a front view of an electromagnetic line switch having the auxiliary time delay controlling mechanism therefor arranged in accordance with the present invention. Figs. 2 and 3 are side views of the electromagnetic circuit protective device of Fig. 1 showingthe relative positions of the controlling elements during different phases of operation. Fig. 4 is a simplified diagram of a control system for an alternating current motor embodying the undervoltage protective device of the present invention.

In Fig. 1 the circuit protective device comprises the electromagnetic switch 10 having the three movable circuit controlling switch members 11 mounted upon the pivoted shaft. 12 operated by the electromagnet 13. The shaft 12 is mounted in suitable supports 14 on-the base or panel 15. The movable magnetic member or armature 16 of the electromagnet 13 is fixedly secured to the operating shaft 12 as indicated in the drawings.

The automatic time delay circuit controlling device 17 for automatically controlling the energizing circuit of the electromagnet 13' after the occurrence of undervoltage condi-.

tions comprises a movable contact 18 which; is normally biased out of engagement with the cooperating contact 19 as shown more in detail in Figs. 2 and 3. The contact 18 is arranged to be closed upon closure of the electromagnetic switch 10 by means of the operating arm 20. The arm 20 engages with the pin 21 extending from the 'member 22 which is pivotally mounted on the shaft 23. The contact 18 is resiliently connected to the pivoted member 22 by the spring 24.

The opening of the contact 18 is delayed by means of a suitable time delay mechanism, such as the inertia flywheel 26, which is connected through the reducing gear 27 to the gear wheel 28. The gearwheel 28 is releasably connected with the pivoted member 22 by means of a spring pressed pawl 29. The pawl is provided with a sloping tooth of such shape as to ride over the teeth of the gear 28 when the pivoted member 22 is operated in a counterclockwise direction to effect closure of the contact 18. The pawl 29, however, positively engages with the teeth on the gear 28 when the pivoted member 22 is released by the opening of the electromagnetic switch 10. With the member 22 released, the strain in the spring 24 causes the member 22 to rotate in a clockwise direction under the retarding action of the inertia flywheel 26. When the strain in the spring 24 has been released, the member 22 engages with the small pin 25 within the spring 24 to operate the switch 18 to the circuit opening position, as shown in Fig. 2.

The circuit protective device shown in Figs. 1 to 4 may be applied to provide automatic time delay undervoltage protection to a motor circuit, as illustrated diagrammatically inFig. 4. As shown in the diagram, the movable contacts 11 of the switch are connected to control the connection and disconnection of the motor M, which is shown as of the 3- phase alternating current type, with the supply lines L. The operating electromagnet 13 is connected to be energized in accordance with the voltage across one phase of the motor circuit under the control of the normally open start push button 30 and the normally closed stop push button 31. The contact 18 of the automatic time delay device is connected to establish a holding circuit for the electromagnet 13 in shunt with the start push button 30 immediately upon closure of the electromagnetic line switch 10. In this way the magnetic armature 16 is maintained attracted to hold the switch contacts 11 in the circuit closing position after the release of the start push button 30.

In case the motor circuit controlled by the electromagnetic switch 10 is subjected to undervoltage conditions the energizing voltage of the electromagnet 13 may be reduced sufficiently to permit the contacts 11 to open in accordance with their bias. The contact 18, however, maintains the electromagnet 13 connected to be energized in accordance with the voltage of the supply lines for a predetermined time interval due to the operation of the inertia time delay flywheel 26 as previously pointed out. Thus in case the undervoltage conditions are only momentary and the voltage of the supply lines L quickly returns to the normal value, the electromagnetic switch 10 is reclosed immediately to continue operation of the motor M. If, however, the undervoltage condition persists for an extended interval sufficient to permit the time delay mechanism functioning, the contact 18 is opened and subsequent automatic reclosure of the electromagnetic switch 10 is effectively prevented. In either case the motor M is protected against continued operation at reduced voltage; It will be evident that the switch 10 may be operated to disconnect the motor M from the supply lines L whenever desired by operation of the stop push button switch 31.

What I claim as new anddesire to secure by Letters Patent of the United States, is,-

1. A time element undervoltage. circuit protective device comprising a switch having a voltage responsive holding means for main: taining the switch closed during normal Voltage conditions and automatically operable to open the switch upon. the occurrence of undervoltage conditions, and time delay switch mechanism controlled by said voltage respons ve holding means for interrupting the energizlng circuit of said voltage responsive holding means a time interval after the occurrence of undervoltage conditions.

2. A time element undervoltage circuit protective device comprising a switch biased to the circuit opening position and having electroresponsive means connected to be energlzed responsively to the voltage of the circu it for operating the switch to and maintaming the switch in the circuit closing position during normal voltage conditions inthe c1rcu1t,and an automatic time element circuit controlling device operated by said electroresponsive means for maintaining said electroresponsive means connected to be energ zed in accordance with the voltage of the circuit until a predetermined time interval after the occurrence and continuance of undervoltage conditions.

3. A time element undervoltage-( circuit protective device comprising a switcli biased to the circuit opening position, electrorespons ve means for operating the switch to. the circuit closing position, means for energizing sa1d electroresponsive means'in accordance with the voltage of the circuit to maintain the switch closed including a time delay circuit controlling device operated by said electroresponsrve means for interrupting the energizmg circuit of said electroresponsive magnet for operating'the switch to the circuit closing position and electromagnetically maintaining the switch therein, a time delay circuit controlling device operable with a time delay to the circuit opening position and connected with said first switch to be operated to the circuit closing position upon closure thereof and connections controlled by said device through which the said electromagnet is energized in accordance with the voltage of the circuit controlled by the switch upon closure of the switch and until a predetermined time interval after the occurrence of undervoltage conditions in the circuit.

5. A time element undervoltage circuit protective device comprising a switch biased to the open position, an electromagnet for operating the switch to the closed position, means for energizing said electromagnet in accordance with the voltage of the circuit controlled by the switch to maintain the switch closed during normal voltage conditions in the circuit, said means including a time delay switch mechanism under the control of said electromagnet and operable to the circuit opening position a predetermined time interval after the opening of the first switch.

6. A time element undervoltage circuit protective device comprising a switch biased to the circuit opening position and having an electromagnet for operating the switch to and maintaining the same in the circuit clos: ing position, a second switch biased to the open-position and connected with the first switch to be operated to the circuit closing position substantially simultaneously with the first switch, time delay mechanism for retarding the opening of said-second switch for a time interval after the opening of the first switch, and connections controlled by said second switch through which the operating electromagnet of said switch is connected to be energized in accordance with the voltage of the circuit controlled by the first switch upon the closure thereof.

7. A time delay-circuit controlling device comprising an electromagnetic switch biased to the circuit opening position, a normally open control switch for momentarily energizing said electromagnetic switch in accordance with the voltage of the circuit controlled thereby to effect operation of the electromagnetic switch to close the circuit, a relatively movable switch associated with said electromagnetic switch for maintaining the same energized in accordance with the voltage of. the circuit controlled thereby a er the clo-' .6 sure thereof, and time delay mechamsm for 'sive means is connected to preventing the opening of said relatively movable switch for a time interval after the opening of said electromagnetic switch due to the occurrence of undervoltage conditions in the circuit controlled thereby.

8. A time element undervoltage protective device comprising two relatively movable. switches each biased to the circuit opening position, electroresponsive means for operating the same to the circuit closing position and maintaining the same therein, time delay mechanism for delaying the opening of one of said switches for a predetermined time interval, and connections controlled by said one switch through which said electroresponbe energized in accordance with the voltage of the circuit controlled by the other switch.

9. A time element undervoltage circuit controlling device comprising two relatively movable switches, each biased to the circuit opening position, electroresponsive means for operating the same to the circuit closing position and maintaining the time delay mechanism for retarding the opening of one of said switches for a predetermined time interval, a normally open control switch for energizing said electroresponslve means in accordance with the voltage of the circuit controlled by the other switch to efi'ect operation of the relatively movable switches to their respective circuit closing positions, and connections controlled by said one switch through which said means is maintained energized in accordance with the voltage of the circuit controlled by said other switch until a predetermined time interval after the occurrence of undervoltage conditions in the circuit.

same therein,

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tromagnet having a magnetic element movtion of the electromagnet to close said main contacts, a time element controlling device for maintaining an energizing circuit .for said electromagnet including an auxiliary switch member and a resilient connection between said magnetic element and said auxiliary switch member which is put under strain upon the closure of said main switch contacts able to the attracted position vupon energizato thereby close said auxiliary switch upon I the movement of said magnetic element to the attracted position, and time delay mechanism which delays the release of the strain of said resilient connection to provide for a delay in the return of said auxiliary switch to the open position for a predetermined interval of time. after the release of said magnetic element from the attracted position thereof.

In witness whereof, I have hereunto set my hand this 15th day of Februar 1927.

. GEORGE R.- TO SEND. 

